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M Tsuboi

Publications and source records attributed to M Tsuboi.

At least 145 records · Page 8Linked to original sources
PubMed1989

Beta-adrenergic receptor adaptation after an acute exercise in rat myocardium.

An acute dynamic exercise provokes the translocation of beta-adrenergic receptors (beta-AR) from light vesicle fractions to sarcolemmal membranes in rat myocardium. However, 15 min after an acute exercise the density of beta-AR in both fractions returned to the pre-exercise level. The mean maximal activity of adenylate cyclase in response to isoproterenol roughly paralleled the redistribution of beta-AR. The dose-response curves, however, were substantially shifted to the right with increase in EC50 for isoproterenol stimulation of adenylate cyclase. Thus, the sensitivity of sarcolemmal beta-AR was found to be blunted 15 min afterwards.

Adenylyl Cyclases↗
PubMed1989

Effects of adenosine and pertussis toxin on lipolysis in adipocytes from exercise-trained male rats.

The sensitivity and responsiveness of adipocyte lipolysis to adenosine and pertussis toxin were studied in exercise-trained male rats. Exercise training (9 weeks of treadmill running) significantly increased lipolytic response of adipocytes to noradrenaline (NA). Addition of adenosine deaminase (ADA) to reaction mixture effectively enhanced NA-stimulated lipolysis in adipocytes from both conditioned rats. However, under these conditions, the difference due to exercise training was still evident, although the difference was less pronounced. The inhibition curves of the R-site adenosine analogue N6-phenylisopropyladenosine (PIA) against "basal" (lipolysis in the presence of ADA) and NA-stimulated lipolysis were almost comparable between two groups. Only a small (approx. 2-fold) increase in IC50 of adipocyte lipolysis was observed in each inhibition curve in exercise-trained rats. Within 120 min of addition of pertussis toxin to adipocytes from control rats, "basal" lipolysis was significantly increased as compared to "basal" lipolysis in the absence of toxin at the same point. Similarly, pertussis toxin significantly increased "basal" lipolysis in exercise-trained adipocytes. However these were relatively sensitive to pertussis toxin, since significant effect of toxin was seen within 60 min. An addition of NA (0.1 uM) to the medium in the presence of ADA and toxin significantly increased adipocyte lipolysis in both conditioned rats. Again, under these conditions, we observed that the maximal rate of lipolysis of adipocytes from exercise-trained rats was increased as compared to control rats. These results suggest that the decreased input through the inhibitory pathway in lipolytic cascade may be not rate limiting for the amplified lipolytic responsiveness of adipocytes to hormonal stimuli in exercise-trained rats.

Adenosine↗
PubMed1989

[A case of facial nerve neurinoma originated from the cerebellopontine angle portion].

Facial nerve neurinomas are relatively rare and most of them appear at the vertical portion of the facial nerve. Facial nerve neurinoma originated from the cerebellopontine (c-p) angle portion is less frequently reported. A 51-year-old woman was admitted to our hospital complaining of severe headache and nausea. She had had dizziness and unsteady gait for the previous two weeks. She did not complain of hearing disturbance, but otological examination revealed sensorineural deafness. She had no facial palsy. Skull x-ray showed no erosion of the internal auditory canal. Plain CT-scan revealed a large, unenhanced, low-density mass in the right c-p angle cistern. At the time of the operation, this tumor originated from the right facial nerve. Histological diagnosis of this tumor was schwannoma. After the operation, right facial nerve palsy appeared but hardness of hearing was no worse than previously. This tumor seemed to be facial nerve neurinoma in the c-p angle cistern. To the present, 121 facial nerve neurinomas have been reported in the previous literature. Facial nerve neurinomas in the c-p angle cistern, however, have only been reported in 5 cases. The most frequent symptom of facial nerve neurinoma in the temporal bone is facial nerve palsy, but that of facial nerve neurinoma in the c-p angle cistern is hearing loss, as in an acoustic neurinoma. Preoperative diagnosis of facial neurinoma in the c-p angle cistern using neurological symptoms alone is difficult. Furthermore, differential diagnosis from acoustic neurinoma in the c-p angle cistern using only skull x-rays and CT-scanning is also difficult.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebellar Neoplasms↗
PubMed1989

Inhibition of immune haemolysis by a serum factor found in C3-deficient subjects.

A serum factor, which inhibits haemolysis of the buffer control used in a C3 haemolytic assay, was found in a C3-deficient subject (C3D). Since the buffer control consisted of EAC142, C5 and C6-9 reagent (C6-9R, prepared by treatment of guinea-pig serum with KSCN and hydrazine hydrate), the factor seems to be an inhibitor of C3-independent immune haemolysis. Gel filtration and CM cellulose column chromatography of C3D serum suggested that the inhibitor may be C8. The inhibition was not observed in C8-depleted C3D serum. Furthermore, isolated C8 was found to inhibit haemolysis of EAC142 by C5 and C6-9R in a dose-dependent fashion. Thus, C8 was found to be an inhibitor of C3-independent immune haemolysis in the assay. Further studies revealed that C8 also inhibits haemolysis of EAC142 by C3, C5 and C6-9R (C3 assay system) or that of EAC1423 by C5 and C6-9R (C5 assay system), indicating that C3 or C5 haemolytic activity can be underestimated by the presence of C8 in a sample. C8 did not inhibit haemolysis in the assay system when isolated C6-C9 of human origin were used, but did inhibit haemolysis when isolated C6-C9 of guinea-pig origin was used instead of C6-9R. Thus, it was suggested that the incompatibility of human C8 with guinea-pig C6-C9 might be responsible for this phenomenon. Additional experiments for the mechanism clearly showed that human C8 inhibits the haemolysis of EAC1-7 (EA bearing human C1-C5 and guinea-pig C6 and C7) by guinea-pig C8 and C9 by binding to EAC1-7 prior to guinea-pig C8.

Animals↗
PubMed1988

Possible mechanism of regulating adenylate cyclase activity in adipocyte membranes from exercise-trained male rats.

(-)-Isoproterenol-stimulated adenylate cyclase activities were significantly greater in membranes from exercise-trained male rats than in sedentary male rats. GTP-inhibition of forskolin (10 microM)-stimulated cyclase activities were observed in sedentary membranes, whereas the inhibitory actions of GTP were significantly reduced in membranes from trained rat adipocytes. Treatment of membranes with islet-activating protein, a pertusis toxin, completely abolished the differences in GTP-inhibition of forskolin-stimulated cyclase activities between the two groups. The amounts of the inhibitory regulatory protein (41kDa/40kDa polypeptides) were about 40% less in membranes from trained rats than in sedentary membranes, whereas that of the stimulatory regulatory protein (a 45kDa polypeptide) was equivalent. It is concluded that the enhanced cyclase activities of adipocyte membranes from trained male rats appear to result from, in part, an attenuation of the inhibitory pathway due to a specific decrease in the amount of the inhibitory regulatory proteins.

1-Methyl-3-isobutylxanthine↗
PubMed1988

Studies on the formation of a unique cellular intermediate (EAC14256) from EAC142 and C56.

The binding reaction of C56 to EAC142 was studied. The following was observed: (1) C56 can bind to EAC142, without participation of C3 or C7, to form EAC14256; (2) the efficiency of EAC14256 formation from EAC142 and C56 depends highly on the ionic strength of the buffer; (3) EAC14256, generated from EAC142 and C56, decays spontaneously by elution of C56 into the medium and thus the reaction between C56 and EAC142 is reversible; (4) the receptor on EAC142 for C56 is C2 or C42 on the cell surface, and (5) the binding of C56 to C2 or C42 on cells is independent of the usual (C3-dependent) complement cascade activation. These observations, together with the results of our previous report, indicate that the binding of C56, generated from the activation of C5 by C42 (without C3), to EAC142 may be the initial step of membrane attack complex formation in C3-independent immune hemolysis.

Antibodies↗
PubMed1988

Effects of cyclic nucleotide derivatives on the Na+ pump activity and the release of sialic acid in dog submandibular glands.

The effects of dibutyryl cyclic AMP (DBcAMP) and cyclic GMP (DBcGMP) on the Na+,K+-ATPase activity and the release of sialic acid were investigated in dog submandibular gland pieces. The Na+,K+-ATPase activity and the release of sialic acid were significantly stimulated in the presence of 100 microM DBcAMP or in the combination of 3 mM NaF and 50 microM 1-methyl-3-isobutylxanthin but were not by DBcGMP. When the pieces were incubated in the Ca2+-free medium, the DBcAMP-induced Na+,K+-ATPase activity slightly decreased but the sialic acid release was unaffected. The corresponding results were also observed in the Ca2+-free medium supplemented with 2 mM EGTA. These results suggest that the cytosolic cyclic AMP modifies the Na+ pump activity.

Animals↗
PubMed1988

Some characteristics of the beta-adrenergic system in rat adipocyte membranes after the chronic administrations of isoproterenol.

The effects of chronic administrations of isoproterenol (IPR) on adipocyte beta-adrenergic system were investigated. A 21-days in vivo administration of IPR (2.5 mg/kg BW/day) reduced (-)-IPR- and 5'-guanylylimidodiphosphate-stimulated adenylate cyclase activities. Moreover, the number of beta-adrenergic receptors (beta-AR) and (-)-IPR-stimulated [3H]GDP release from adipocyte membranes were significantly depressed in the treated rats compared to controls. These results suggest that the desensitized response of adenylate cyclase to beta-agonists, induced by chronic in vivo administrations of IPR, may result from impaired coupling efficiency between beta-AR and adenylate cyclase with the significant loss of the number of beta-AR and possible change(s) of guanine nucleotide regulatory proteins.

Adenylyl Cyclases↗
PubMed1987

Two types of conformers with distinct Fe-C-O configuration in the ferrous CO complex of horseradish peroxidase. Resonance Raman and infarared spectroscopic studies with native and deuteroheme-substituted enzymes.

The presence of at least two types of conformers in the ferrous CO complex of horseradish peroxidase has been demonstrated with the use of native and deuteroheme-substituted enzymes. Type I conformers, predominant in acidic pH, exhibited both an Fe-CO stretching and an Fe-C-O bending Raman line together with an infrared C-O stretch band below 1920 em-1. On the other hand, type II conformers, dominant species in alkaline pH, showed only an Fe-CO stretching Raman line with the C-O stretch above 1930 cm-1. They were interconvertible either by the changes in pH or by the binding of benzhydroxamate, a substrate for the enzyme. The pKa value for the pH-dependent interconversion of CO complex of deuteroheme-substituted enzyme was 8.3. These findings were interpreted to mean that the bound CO molecule in type I conformers was more tilted over the heme-plane than that in type II conformers. A steric hindrance by the bound substrate or the protonated form of a distal amino acid residue, presumably of histidine, is considered to be the cause for the isomerization. By summarizing present and previous data on the vibrational frequencies of heme-carbonyl complexes, we found that there are inverse-linear relationships between the square of Fe-CO and that of C-O stretching frequencies, while squares of Fe-CO stretching and Fe-C-O bending frequencies were linearly correlated with each other. Also found is that the dissociation rate constant of CO molecule from heme-carbonyl complexes is a linear function of the Fe-CO stretching frequency. The significance of these results is discussed.

Carbon Monoxide↗
PubMed1987

Multidimensional stopped-flow photometry monitoring initial processes of platelet activation.

A group of initial processes in platelet activation, consisting of a platelet shape change, an intracellular calcium mobilization, a calcium efflux, and a membrane fluidity (mobility) change, has been examined in rabbit platelets by a multidimensional stopped-flow method with light scattering, light transmission, and fluorescence measurements. It was found that a 90 degrees light scattering change and internal calcium release (monitored in terms of chlortetracycline fluorescence) take place after a short lag (5 s at 25 degrees C and 2 s at 37 degrees C) following activation by thrombin. The duration of the lag was the same in both cases. During the initial lag period, a rapid increase in platelet membrane fluidity (mobility) was observed by the use of pyrene excimer fluorescence. These results suggest that the intracellular calcium mobilization and the shape change are triggered by the same rate-determining step, and increase in membrane mobility may play some role in the initial stage of platelet activation before intracellular calcium mobilization occurs.

Animals↗
PubMed1987

Effects of monensin on the Na+ pump activity and the release of amylase and sialic acid in dog submandibular glands.

The effects of monensin on the Na+,K+-ATPase activity and the release of amylase and sialic acid were investigated in dog submandibular gland pieces. Monensin stimulated the Na+,K+-ATPase activity and amylase release in a dose-dependent manner. Moreover, this agent increased the Na+,K+-ATPase activity and the release of amylase and sialic acid induced by pilocarpine. These results suggest that monensin increases the release of amylase and sialic acid in dog submandibular glands, in part, through the Na+ pump activated due to the Na+ influx.

Amylases↗
PubMed1987

Effects of Ca2+ and calmodulin antagonists on the Na+ pump activity induced by pilocarpine in dog submandibular gland.

The effects of Ca2+ and calmodulin antagonists on the Na+,K+-ATPase activity were investigated in dog submandibular gland pieces. The Na+,K+-ATPase activity of the gland pieces which were incubated in the presence of 5 microM A23187, a Ca2+ ionophore, was about 2-fold of that seen in the control medium. Verapamil, diltiazem and La3+ (Ca2+ antagonists) and chlorpromazine, trifluoperazine and W-7 (calmodulin antagonists) had no significant effect on the Na+,K+-ATPase activity in the control medium, but significantly inhibited that induced by pilocarpine. These results suggest that the Na+ pump activity is modified by the Ca2+ influx from the extracellular spaces and the intracellular Ca2+-calmodulin complex.

Animals↗
PubMed1987

Does calmodulin participate as an intermediate in the process of glycogenolysis in rat submandibular gland?

A role of calmodulin in the process of the glycogenolysis induced by adrenaline was investigated in rat submandibular gland. When the slice was incubated in the Ca2+-free medium, the adrenaline-induced glycogenolysis was significantly inhibited. Moreover, the inhibition of glycogenolysis induced in the Ca2+-free medium was further enhanced by addition of 2 mM EGTA. Chlorpromazine, trifluoperazine and W-7, calmodulin antagonists, had no effect on the glycogenolysis induced by adrenaline. These results suggest that the adrenaline-induced glycogenolysis is dependent on the presence of Ca2+ and that calmodulin does not participate in the process of glycogenolysis in rat submandibular gland.

Animals↗
PubMed1986

Local and overall conformations of DNA double helices with the A - T base pairs.

Raman spectra have been observed of two different poly[d(A-T)].poly[d(A-T)] fibers, whose X-ray diffractions were confirmed to be purely of A and B forms. A number of spectral differences were found between the A and B forms of this DNA duplex, and they were ascribed to local conformational differences in the adenosine, thymidine and phosphodiester portions. The ascription was made on the basis of a separate series of Raman examinations on six crystals involving adenosine or thymidine, and fifteen other nucleotide crystals, whose structures are all known by previous crystallographic works. By taking these structure-spectrum correlations thus obtained into account, a Raman spectroscopic investigation was made of a few double-helical DNAs in aqueous solutions. It has been concluded that both poly[d(A-T)].poly[d(A-T)] and poly(dA).poly(dT) have a C2'endo-anti adenosine, C2'endo-anti thymidine, a b-type mainchain (beta = 160 +/- 15 degrees, gamma = 45 +/- 15 degrees, delta = 140 +/- 10 degrees) and an a2-type mainchain (beta = 210 +/- 10 degrees, gamma = 45 +/- 15 degrees, delta = 140 +/- 10 degrees) not only in low-salt medium but also in 6.6 M CsF solutions, where beta, gamma and delta are the torsion angles around O5'-C5', C5'-C4' and C4'-C3' axes, respectively. Poly(rA).poly(dT), on the other hand, was considered to have a heteronomous duplex structure, in which the poly(rA) strand has a C3'endo-anti adenosine and a1-type mainchain (beta = 175 +/- 25 degrees, gamma = 45 +/- 15 degrees, delta = 80 +/- 10 degrees) whereas the poly(dT) strand has a C2'endo-anti thymidine and b-type mainchain.

Adenosine↗